The present invention relates to a signal detecting device for detecting a difference signal for an electrical measurement of a vital parameter of a living being, for example an ECG measurement, to an electrode arrangement as may exemplarily be arranged in a motorcar (MC), and to a method.
The heart, being one of the most important organs of the human organism, represents a broad basis for diagnosing most different diseases in medicine. Electrical potentials form on the body's surface caused by the three-dimensional propagation of the excitation in the heart. Detecting temporal changes of potential differences between defined positions on the body's surface is referred to as electrocardiography. The recording of the potential lines resulting is referred to as electrocardiogram, abbreviated as ECG.
The electrical potentials are, for detecting the ECG, fed to high-resistance amplifiers via electrodes on the body's surface. The potentials to be recorded are of an amplitude of 50 μV-5 mV and comprise frequency components in the range from 0.1 to 150 Hz. The ECG is recorded via electrodes on the thorax or arms as a standard. Depending on the number of channels to be recorded, the number of electrodes typically varies between three and ten.
At present, there are various forms of ECGs, a particular difference here being the application time. Short-term ECGs serve for quickly diagnosing the heart's function, whereas prolonged ECGs are able to record the heart's function over a longer period of time. In contrast to body function monitoring devices which are also available for end users, such as, for example, pulse watches, electrocardiographs for recording ECGs are frequently operated by physicians only due to their complexity. Here, electrodes via which the potential differences can then be measured are applied to the body of a human being following a certain principle. The individual electrodes applied to the body are connected via cables to evaluating means which detect the changes in potential differences over time.
Several systems are known for increasing traffic safety, which allow estimating the mental and physical state of the driver on the basis of his vital parameters measured in the vehicle. Conclusions from such systems may be applied in the following fields: diagnosis and/or therapy support, recognizing emotions, concentration of the driver, tiredness and sleepiness, and quantization of vegetative stress levels.
Some systems also offer a way of acting on the control units of the automobile depending on the state of the driver established. These systems are usually referred to as: health monitoring systems, driver assistance systems, body state measuring means, vehicle safety devices and therapeutic systems.
DE 102 49 415 B3 describes a system for supporting the diagnosis, therapy and/or preventive treatment of a person in the vehicle. Sensory monitoring of the patient here means measuring weight and respiratory rate.
WO 98/25520 describes a security device for detecting, warning and preventing decreasing concentration of the vehicle driver and for warning or preventing sleepiness. The document cited also suggests implementing an emotion detector system. The physical measuring quantities for this are heart rate, heart rate variability and body temperature which are sampled using electrodes on the steering wheel, and pulse which is sampled using pulse measuring devices on the surface of the steering wheel.
WO 02/096694 A1 describes a method and means for characterizing the state of the driver of a motorcar, the control units of the motorcar being influenced using the results established. The concept in accordance with the publication cited takes several physiological state variables, such as, for example, ECG, heart rate, EEG, blood pressure, skin temperature, skin conductivity, eyelid frequency, gripping force and movements of the driver in his seat, into account.
DE 10 2005 007 963 A1 describes a method and means for quantizing a vegetative stress level. The document cited describes determining the vegetative stress level also under automobile conditions by means of heart rate monitoring. Recording the heart rate may in this case be done using sensors or sensor fields which are integrated in the operating devices—steering wheel, gear shift lever—of a vehicle.
DE 60124971 T2 describes a health monitoring system. The system suggested may, among other things, be used for monitoring the person in the vehicle. The measuring quantities here are heart rate data recorded by plate electrodes on the steering wheel, secretion of sweat recorded by sweat sensors (term used by the inventor) on the steering wheel, and the video image of a camera. The health monitoring system is optimized for monitoring several persons at the same time.
GB 2 390 460 A describes a tiredness alerter which determines a driver's tiredness level using his body temperature, pulse rate, blood pressure and oxygen saturation in the blood.
DE 10 2004 036 119 B4 describes a driver assistance system for recognizing tiredness and evaluating the attentiveness of a driver using his pulse frequency. The sensors for detecting the pulse frequency are, in accordance with the document cited, to be integrated in the steering wheel, gear selecting lever or seat.
DE 602 14 312 T2 describes an apparatus for measuring the state of a driver's body. The following vital parameters are detected here: pulse, sweat secretion, skin resistance, respiration, heart rate and heart rate variability. Embodiments thereof are the following variations:    a) body state measuring means for determining whether the operator is in a “steady state”,    b) body state measuring means and interaction thereof with a navigation system, and    c) body state measuring means and interaction thereof with a music system.
One disadvantage of many diagnostic methods for the cardiovascular system when being used under automobile conditions, but also in diagnostics, for example when seeing a physician, is that they are either of invasive character or that application parts thereof (electrodes and leads thereof) have to be applied to the body before measuring and be connected to signal evaluating electronics.
Most known systems for monitoring drivers by means of vital sensor technology (such as, for example, pulse measurements or ECG) are only described too generally and ignore important aspects such as: signal quality, coverage of the passenger area with sensors, probability and frequency of sensor contacts by the driver, diverting the driver by the interaction with the measuring system and potentially resulting impairment of driving safety, and build-up time of the sensors, i.e. how fast the sensors are able to provide valid data after being touched.
Some health assistance systems promise the possibility of diagnosing or diagnosis support, preventive treatment or even therapy support when being used in automobiles. However, up to now there are no systems known on the market which are really able to record vital data in automobiles for diagnostics and therapy support with the precision needed. This may be explained by the challenging fringe conditions and the lack of acceptance on the part of the driver (sensor on the body) in the automobile environment.
Possible systems for detecting a vital parameter of a living being, such as, for example, an ECG, may be provided with a plurality of electrodes, the plurality of electrodes generating difference signals from which an ECG can be derived. This means that the quality of the ECG is strongly dependent on the signal strength of the electrodes.